Heat transfer process



June 28, 1966 J. K. LA FLEUR 3,258,508

HEAT TRANSFER ?ROCESS Filed June 1, 1964 2;1. a L 8 4, -il COMBUSTION CHAMBER HOT INVENTOR Jia/wes K. La FLEUQ 6o BY iwf/:LLM-

ATTO 2 N E V United States Patent O 3,258,508 HEAT TRANSFER PROCESS James K. La Fleur, Hermosa Beach, Calif., assignor to The La Fleur Corporation, Los Angeles, Calif., a corporation of California Filed June 1, 1964, Ser. No. 371,428 12 Claims. (Cl. 263-52) This invention relates to a proces for heating gases employing combustion gases as a heat transfer medium, and is particularly concerned with an efficient proces for heating a compressed propulsive gas, such as helium, to be used for driving a turbine in a closed cycle gas turbine v power plant, utilizing hot combustion gases which are compressed in -a compressor 10, then heated in a hot regenerator 12, and passed to a combustion chamber heat exchanger 14. In the exchanger 14, the helium is further heated to a high temperature for introduction into a hot turbine 16 which functions to supply power to the-compressor 12. The expanded helium leaving turbine y16 then is recycled via the hot `regenerator 12 and back to the compressor for recompression. In the system described in my above copending applications, such power cycle is employed for driving a refrigeration cycle also employing helium as the working system (not shown). In the system illustrated in FIG. l of the drawing, the numeral 18 indicates hot combustion gases which are passed into heat exchange relation with the helium in the exchanger 14, and the numeral 20 represents exhaust gases from the exchanger.

For purposes of illustration, according to one mode of procedure for operation of a closed cycle gas turbine power system utilizing helium as the working uid, helium gas enters the heater 14 at approximately 1000 F. and is heated therein to about 1200i F. Hot combustion gases are introduced at 18 in FIG. 1 into the heat exchanger 14 for purposes of heating the helium to the above-noted approximately 1200 F. However, allowing the hot combustion products to impinge upon the heat exchanger tubes at temperatures much above 1800 F. results in costly and short-lived heat exchangers.

In conventional systems of this type, since the combustion gases are at the high, approximately 3500 F., ternperature, special heat exchange equipment is usually necessary to prevent direct impingement of such hot gases directly against the tubes, for example, baffle systems which cause heat transfer from the combustion gases to take place essentially by radiation rather than by sweeping the gases directly across the tubes (convection). But this technique is still not sufficient to prevent burning out of the tubes of the exchanger in a relatively short period. Therefore, it is necessary to dilute the combustion gas with fresh air to hold the inlet combustion gas temperature down to the order of about 3000 F.

However, this latter technique is still unsatisfactory because in the first place, the maximum heating value of the fuel is not utilized by such dilution of the combustion gases with fresh air. Further, the spent gases are still at a high temperature and are passed through a preheater to heat the combustion air. However, this is inefficient because more air than is actually required for combustion must then be heated by the combustion of the fuel. Also, the excess air present in the diluted .combustion gases results in a highly oxidizing atmosphere in the heat 3,258,508 Patented .lune 28, 1966 ice exchanger, and this further tends to cause deterioration and burning out of the tubes.

It is an object of the invention to provide a heat transfer procedure for efficiently heating a gas, preferably a preheated gas, utilizing combustion gases which are substantially reduced in temperature and containinga minimum amount of oxygen as heat transfer medium.

A particular object of the invention is to provide a highly efcient heat transfer proces-s for heating a gas, preferably a preheated, compressed propulsive gas, such as helium, for use in a closed cycle gas turbine power systern, employing combustion products which are reduced in temperature substantially below 3500" F. and preferably below l800 F., without employing fresh air as the cooling and diluting medium, said mixture of combustion gases of reduced temperature containing a minimum amount of oxygen.

Other objects and advantages will be apparent hereinafter.

According to the invention, the hot combustion gas is mixed with spent combustion gases previously discharged from the heat exchanger, so as to substantially lower the temperature of the mixture entering the heat exchanger, e.g., down to the order of about 1700 F. This results in preventing undue damage as by burning of the tubes and heat exchanger auxiliary equipment. Further, according to preferred procedure, only enough fresh air is introduced into the combustion chamberto cause substantially complete combustion of the fuel so that the gaseous combustion products contain substantially no excess air or oxygen. Such absence of oxygen in the mixture of hot combustion gases and spent gases used as the heat transfer medium avoids the danger of a highly oxiof the heat exchange equipment which occurs in the presence of an oxidizing atmosphere.

According to one mode of procedure for heating compressed helium according to `the invention procedure, a mixture of hot combustion gases and spent gases from the heat exchanger is introduced into the heat exchanger at an inlet temperature of about 1700 F., as previously noted, and the spent gases leaving the heat exchanger have a temperature of about 1000 F. The helium in such exchanger is heated from an inlet temperature of about 1000 F. to an exiting temperature of about 1200 F. The spent gases at about 1000 F. are thus mixed with the hot combustion gases at about .91500o F. to form the above-noted gas mixture-of about l700 F. By this method of recycling spent gases for admixture with the hot combustion gases, only a quantity of spent gas equal to the amount of fuel and fresh airintroduced for combustion need be exhausted to the atmosphere.

The above-noted invention concept results in a dual economy in that the relatively small amount of spent gas which is exhausted to the atmosphere is at a relatively low temperature of about 1000 F., and a substantial portion of the heat derived from that portion of the spent gas which is recycled and mixed with the hot combustion gases, is retained in the process.- Further economy can be achieved by utilizing the waste or spent gas to preheat incoming fresh airused for combustion, before such waste gas is exhausted to the atmosphere.

A major advantage of the procedure and system of the invention is that the size of the heat exchanger can be greatly reduced because of the lower temperature of 4the diluted combustion gases used as heat transfer medium, which makes it possible to construct compact heat exchange surfaces utilizing thin-walled tubing and greatly reduces the cost of the construction material due to the increased strength of conventional construction metals and alloys below about 1700 F., the operating temperature of the heat exchanger according tothe nivention.

A novel, compact, efficient heat exchanger construction particularly suited for use in the instant process is described and claimed in my copending application Serial No. 371,288, iiled of even date herewith.

The invention will be more clearly understood by reference to a preferred embodiment of the invention described below, taken in connection with the accompanying drawing, wherein FIG. l is a schematic diagram of a closed cycle gas turbine power system in which compressed helium is heated according to the invention procedure for use in driving the turbine;

FIG. 2 represents a schematic flow diagram of a preferred mode of operation for carrying out the invention process; Y

FIG. 3 illustrates a form of apparatus employed in carrying out the invention procedure, and

FIG. 4 shows a plan view detail taken on line 4 4 of FIG. 3.

Referring to FIG. 2 of the drawing, fuel and air for combustion are introduced into a combustion chamber indicated at 22. As previously noted, the amount of air introduced is just about su'cient to cause complete cornbustion of the fuel so that the combustion products exiting the combustion chamber 22 are at a temperature of approximately 3500 F. Such combustion products enter a mixing chamber indicated at 24 where they are mixed with cooled spent combustion gases from the heat exchanger 26 as described below. Such exiting combustion gases can have a temperature ranging from about 900 -to about 1200 F., usually about 1000 F., according to a preferred mode of procedure. The quantities of hot combustion gases at 3500 F. and cooled spent gases exhausted from the heat exchanger and mixed with the hot combustion gases are preferably chosen so that the tempera- `ture of the mixed combustion gases leaving the mixing chamber ranges from about 1500 F. to about 1800 F., preferably approximately l700 F.

The mixture of combustion gases at temperature of about l700 F. is passed into a heat exchanger indicated at 26 in heat exchange relation with a compressed propulsive gas, preferably helium, which has been compressed and preheated as indicated at 12 in FIG. l, prior to introduction of the helium into the heat exchanger 26. Thus, for example, the compressed helium entering heat exchanger 26 can have a `temperature ranging from about 900 'to about ll00 F., e.g., about 1000 F. The helium passes through tubes indicated at 28 in the heat exchanger, in heat exchanger relation with the aforementioned diluted mixture of combustion gases. According to the invention described in my above copending application, Serial No. 371,288, the tubes 28 of the heat exchanger can be thinwalled tubes hanging in the form of a catenary curve. The use of such a heat exchanger containing small diameter tubing suspended in the form of a catenary curve increases the available heat transfer surface for heat exchange purposes and results in the construction of smaller, more compact exchangers than conventional heat exchangers employing conventional tubing.

The helium exiting the tubes 2S of the heat exchanger 26 is heated to a temperature of about 1100 to about 1300 F., e.g., about 1200 F., and is conducted through a turbine as illustrated at 16 in FIG. 1 for driving the compressor 10.

The combustion gases exhausted from the heat exchanger 26 are at a temperature in the range of about 900 to about 1200 F., usually of the order of about 1000 F. If all of these gases were exhausted directly to the atmosphere, very poor economy of fuel would result. Thus,

only la portion of the spent exhaust gases from the heatexchanger is vented to the atmosphere at 30, and the remaining substantial portion of the exhaust combustion gases at a temperature, e.g., of the order of about 1000 F., is recirculated to the mixing chamber 24 for admixture with hot combustion gases at a temperature greater than about 3000 F., e.g., about 3500 F., as described above, for producing the heat exchange gas mixture of approximately 1700o F. According to this procedure, only the quantity of exhaust gas equal to the amount of fuel and fresh air introduced in the combustion chamber 22 need be exhausted to the atmosphere. Thus, thermodynamically,v on the basis of a temperature drop of the combustion gases through ythe heat exchanger 26, of from 1700 F. to 1000 F. as noted above, and of a temperature rise through the combustion chamber 22 of approximately 3500 F., this means that only about one-fifth of the combustion gases leaving the heat exchanger 26 is exhausted to the atmosphere, and that the remaining major portion, or about four-fifths, of said combustion gases is recirculated, and such recirculated portion of combustion gases is accordingly approximately four times the amount of the total of fresh air and fuel introduced into the combustion chamber.

To effect further economy in operation, if desired, instead of venting a portion of the exhaust gases directly to atmosphere at 30, such portion of exhaust gases can Ibe passed trhough an air preheater 32 in heat exchange relation with incoming combustion air to preheat such air to a temperature above about 250 F., e.g., up to as high as about 750 F., prior to introduction thereof into the com'bustion chamber 22, as indicated in dotted lines in FIG. 2.

Referring now to FIG. 3 of the drawing, illustrating an apparatus which can be employed for carrying out the invention procedure, air and fuel are introduced into a conventional burned indicated generally at 34, and the hot combustion products are discharged via a nozzle 36 into a conically shaped com-bustion chamber 38 located in the lower portion of the vessel 44.

Exhaust gases from the heat exchanger 50, e.g., at a temperature of about 1000 F., as noted above, are conveyed through a conduit 40 into the space between the conical wall of the combustion chamber 38 and the wall 42 of the vessel `44 in which such combustion chamber 38 is positioned.

The hot combustion gases flowing upwardly from the I conical combustion chamber 38, and the exhaust gases passing upwardly from around the combustion chamber 38 are intermixed in the upper portion of the vessel 44 which constitutes a mixing chamber 46. A mixture of hot combustion gases and spent gases, now at a temperature of about 1700 F., is conducted via a pipe 48 into the heat exchanger 50, and such combustion gases functioning as heat transfer medium, pass ldownwardly through the heat exchanger across banks of suspended catenary tubes 52 supported by headers 54 and 56, such tubes carrying the helium gas to be heated. The construction of such tubes 52 in the form of a catenary, as previously noted, is the subject of the invention of my above copending application Serial No. 371,288.

The preheated helium at a temperature, e.g., of about 1000 F., is introduced via the header 54 into the tubes 52, and after passage through such tubes in heat exchange relation with the aforementioned hot combustion gases, the existing heated helium, e.g., at a temperature of about 1200 F., is discharged into the header 56 from which 'such heated compressed helium is conducted to a turbine, e.g., as indicated at 16 in FIG. 1, for driving same.

The combustion gases exiting the lower end of the heat exchanger, e.g., :at a temperature of about 1000 F., pass into a pipe 58. A portion of such gases is exhausted to the Vatmosphere by a vent 59, while the remainder of such exhaust gases is circulated by a fan indicated at `60 through the conduit 40 and into the lower end of vessel 44 around the combustion chamber 38, as previously described.

Although the instant invention has been described principally in relation to the heating of compressed helium, it will be understood that the invention procedure is applicable to the heating of any gas, and preferably one which has been previously preheated, and which requires further heating, particularly a preheated compressed gas, e.g., for use in a closed c'ycle gas turbine power system.

Thus, the invention in its broader sense comprises mixing hot combustion gases at a high temperature with cooled combustion gases at a reduced temperature, passing the resulting mixture of gases at an elevated temperature intermediate said high temperature `and said reduced temperature into `a zone in heat exchange relation with a gas to be heated, .and which preferably has been preheated to a temperature below the temperature of said mixture of combustion gases, heating said preferably preheated gas and cooling said mixture of combustion gases, discharging said cooled mixture of combustion gases from said zone, venting a portion of said cooled combustion gases either directly to the atmosphere or through an air preheater and then to the atmosphere, `and recirculating the remainder of said cooled combustion gases for admixture with said hot combustion gases as aforesaid.

From the foregoing, it is seen that the invention provides .a novel and efficient system particularly designed for the heating of gases, especially compressed propulsive gases, for use in closed cycle gas turbine power systems.

While I have described particular embodiments of my invention for the purpose of illustration, it should be understood that various modicatitons and adaptations thereof may be made within the spirit of the invention, asset forth in the appended claims.

I claim:

1. The process which comprises mixing hot combustion gases at a high temperature with a substantial portion of cooled combustion gases ata reduced temperature, and substantially reducing the temperature of said combustion gases, passing the resulting mixture of gases at an elevated temperature intermediate said high temperature and said reduced temperature into a unitary zone in heat exchange relation with a gas to be heated, heating said last-mentioned gas and cooling said mixture of combustion gases, discharging said cooled mixture of combustion gases from sai-d Zone, and recirculating a major portion of said cooled combustion gases for vadmixture with said hot combustion gases as aforesaid.

2. The process which comprises mixing hot combustion gases ata high temperature with a substantial portion of cooled com'bustion gases ata reduced temperature, and `substantially reducing the temperature of said combustion gases, passing the resulting mixture of gases at an elevated temperature intermediate said high temperature and said reduced'temperature into a unitary zone in heat exchange relation with a gas to be heated, further heating said last-mentioned gas and cooling said mixture of combustion gases, discharging said cooled mixture of combustion gases from said zone, utilizing a portion of said cooled combustion gases for preheating air for cornbustion to produce said hot com-bustion gases, and recirculating the remaining major portion of said cooled combustion gases for admixture with said hot combustion gases as aforesaid. t

3. The process which comprises mixing hot combustion gases at a high temperature with a substantial portion of cooled combustion gases at a reduced temperature, and substantially reducing the temperature of said combustion gases, passing the resulting mixture of gases at an elevated temperature intermediate said high temperature and said reduced temperature into a unitary single pass zone in heat exchange relation with a gas preheated to a temperature below the temperature of said mixture of combustion gases, and further heating said preheated gas and cooling said mixture of combustion gases, discharging said cooled mixture of combustion gases from said zone, venting a portion of said cooled combustion gases to the atmosphere, and recirculating the remaining major por- 6 tion of said cooled combustion gases for admixture with said hot combustion gases as aforesaid.

4, The process for heating a gas, which comprises introducing fuel `and air into a combustion chamber, the amount of air being only approximately sufficient to cause substantially complete combustion of the fuel, and producing combustion gases at high temperature, mixing said hot combustion gases with a substantial portion of cooled combustion gases at a reduced temperature, and substantially reducing the temperature of said combustion gases, passing the resulting mixture of gases at an elevated temperature intermediate said high temperature and said reduced temperature into a unitary zone in heat exchange relation with a gas preheated to a temperature below the temperature of said mixture of combustion gases, and further heating said preheated gas and cooling said mixture of combustion gases, ldischarging said cooled mixture of combustion gases from said zone, and discharging said heated gases from said Zone, said discharged combustion gases being cooled to a temperature in the range between the temperature of said preheated gas introduced into said zone and the temperature of said preheated gas discharged from said Zone, passing a portion of said cooled combustion gases into heat exchange relation with fresh air for preheating same, employing said preheated air for combustion of fuel as aforesaid, and

recirculating the remaining major portion of said cooled combustion gases for ladmixture with said hot combustiion gases as aforesaid.

5. The process for heating -compressed helium, which comprises introducing fuel and air into .a combustion chamber, the amount of air being only approximately suffcient to cause substantially complete combustion of the fuel, `and producing combustion gases at high temperature, mixing said hot combustion gases with a substantial portion of cooled combustion gases at a reduced temperature, and substantially reducing the temperature of said combustion gases, passing the resulting mixture of gases at an elevated temperature intermediate said high temperature `and said reduced temperature into a unitary zone in heat exchange relation with compressed helium preheated to a temperature 4below the temperature of said mixture of combustion gases, and further heating said preheated helium and cooling said mixture of com- 'bustion gases, discharging said cooled mixture of combustion gases from said zone, and discharging said heated helium from 4said Zone, said discharged combustion gases being cooled to a temperature in the range between the temperature of said preheated helium introduced into said zone and the temperature of said heli-um discharged from said zone, venting a portion of said cooled combustion gases to the atmosphere, and recirculating the remaining major portion of said cooled combustion gases for admixture with said hot combustion gases as aforesaid.

`6. The process for heating compressed helium, which comprises introducing fuel and air into a combustion chamber, the amount of air being only approximately sufcient to cause substantially complete combustion of the fuel, land producing combustion gases at high temperature, mixing said hot combustion gases with a substantial portion of cooled com-bustion gases at ,a reduced temperature, and substantially reducing the temperature of said combustion gases, passing the resulting mixture of gases at an elevated temperature intermediate said high temperature and said reduced temperature into a unitary zone in heat exchange relation with compressed helium preheated to Ia temperature below the temperature of said mixture of combustion gases, and further heating said preheated helium and cooling said mixture of combustion gases, discharging said cooled mixture of combustion gases from said Zone, .anddischarging said heated helium from said zone, said discharged combustion gases being cooled to a temperature in the range between the temperature of said preheated helium introduced into said zone land the l ltemperature of said helium discharged from said zone,

7 passing a portion ofv said cooled combustion gases into heat exchange relation with fresh air for preheating same, employing said preheated .air for combustion of fuel as aforesaid, and recirculating the remaining major portion of said cooled combustion gases for admixture with said hot combustion gases as aforesaid.

7. The pr-ocess for heating compressed helium for operation of a turbine, which comprises introducing fuel and air into 1a combustion chamber, the amount of air being only approximately suicient to cause substantially complete Acombustion of the fuel, and producing hot combustion gases at temperature in excess of 3,000 F., introducing said hot combustion gases anda substantial portion of cooled combustion gases at la `temperature between about 900 F. and about 1200 F. into a mixing zone, to form a mixture of combustion gases at 'a temperature between about 1500o F. and 1800 F., introducing compressed helium pheheated to a temperature between about 900 and about 1l00 F. int-o a heat exchange zone, introducing said mixture of combustion gases into said last-mentioned z-one in heat exchange relation with said lcompressed preheated helium, and further heating said heli-um and cooling said mixture of combustion gases, discharging said heated helium Iheated to a temperature between -about 1100 land about 1300 F. from said heat exchange zione, venting a portion of said cooled combustion gases to the atmosphere, the amount of such gas so vented being substantially equal to the amount of said fuel and air consumed, and recirculating the remainder of said cooled combustion gases for admixture with said hot combustionvgases as aforesaid.

8. The process for heating compressed helium for operation of a turbine, which comprises introducing fuel rand air into a combustion oha'mber, the amount of air being only approximately suicient to cause substantially complete combustion of the fuel, and producing hot `combustion gases at temperature in excess of 3000 F., introducing said hot combustion gases and a substantial lportion :of cooled combustion gasesat a temperature between about 900 F. and about 1200 F. into a mixing zone, to form a mixture of combustion gases at a temperature between about 1500 F. and 1800 F., introducing compressed helium preheated to la temperature between about 900 and about 1100 F. into a heat exchange zone, introducing said mixture of ycombusti-on gases into said last-mentioned zone in heat exchange relation with said compressed preheated helium, and further heating said helium and cooling said mixture of combustion gases, discharging said heated helium heated to a tempenature between about 1100 and about 1300 F. from said heat exchange zone, passing a portion of said cooled combustion gases into heat exchange relation with air Ffor preheating same, employing said vpreheated air for combustion of fuel as aforesaid, and exhausting the exiting combustion gases to the atmosphere, the amount of such gas so exhausted being substantially equal to the amount of said fuel and air consumed, and recirculating the remainder of said cooled combustion gases for admixture with said hOt Combus tion gases as aforesaid,

9. The process for heating compressed helium, which comprises introducing fuel and air into a combustion chamber, the amount of air being only approximately suicient to' cause substantially complete combustion of the fuel, and producing hot combustion gases at a temperature of about 3500 F., introducing said hot combustion gases and a substantial portion of cooled combustion gases at ra .temperature of about l000 F. into a mixing zone to form a mixture of combustion gases at a temperature of about 1700 F., introducing compressed helium preheated to a temperature of about 1000 F. into a unitary heat exchange z-one, introducing said mixture of lhot combustion gases into said last-mentioned zone in heat exchange relation with said compressed preheated helium, and further heating said helium and cooling said mixture o-f combustion gases, discharging said heated compressed heli-um heated to a temperature of about 1200*7 F. from said heat exchange zone, venting a portion of-said cooled combustion gases to the atmosphere, the amount of such gas so Vented being substantially equal to the amount of said fuel and air consumed, land recirculating the remaining major portion of said cooled combustion gases for admixture with said hot combustion gases as aforesaid.

10. The process for heating compressed helium for operation of a turbine, which comprises intro'ducing fuel and air into a combustion chamber, the amount of air being only approximately suicient to `cause substantially complete :combustion of the fuel, and producing [hot combustion gases at a temperature of about 3500 F., introducing s-aid hot combustion gases and a substantial portion of cooled combustion gases at a temperature of about 1000 F. into a mixing zone to form a mixture of combustion gases at a temperature of about 17007 F., introducing said mixture of hot com-bustion gases into said last-mentioned zone `in heat exchange relation with said compressed preheated helium, and further heating said helium and cooling said mixture of combustion gases, discharging said heated helium heated to a temperature of about 1200 F. from said iheat exchange zone, passing a portion of said cooled combustion gases into heat exchange relation with air for preheating same, employingsaid preheated air for combustion of fuel as aforesaid, and exhausting the exiting combustion `gases to the atmosphere, the amount of such gas so exhausted being substantially equal to the amount of said fuel and air consumed, and recirculating the remaining major portion of said Icooled combustion gases for admixture with said 'hot combustion gases as aforesaid.

11. A process as defined in claim 1, wherein said gas to be heated is helium.

12. A process Ias defined in claim 2 wherein said gas to be heated is helium.

References Cited bythe Examiner UNITED STATES PATENTS 2,495,550 l/1950 Ruegg 126-109 2,524,637- 10/1950 Ruegg 126-109 JAMES W. WESTHAVER, Primary Examiner. 

1. THE PROCESS WHICH COMPRISES MIXING HOT COMBUSTION GASES AT A HIGH TEMPERATURE WITH A SUBSTANTIAL PORTION OF COOLED COMBUSTION GASES AT A REDUCED TEMPERATURE, AND SUBSTANTIALLY REDUCING THE TEMPERATURE OF SAID COMBUSTION GASES, PASSING THE RESULTING MIXTURE OF GASES AT AN ELEVATED TEMPERATURE INTERMEDIATE SAID HIGH TEMPERATURE AND SAID REDUCED TEMPERATURE INTO A UNITARY ZONE IN HEAT EXCHANGE RELATION WITH A GAS TO BE HEATED, HEATING SAID LAST-MENTIONED GAS AND COOLED SAID MIXTURE OF COMBUSTION GASES, DISCHARGING SAID COOLED MIXTURE OF COMBUSTION GASES FROM SAID ZONE, AND RECICULATING A MAJOR PORTION OF SAID COOLED COMBUSTION GASES FOR ADMIXTURE WITH SAID HOT COMBUSTION GASES AS A FORESAID. 